For data communication in a network, the data to be communicated is routed through the network, i.e. the data or data packets thereof are directed via data links of the network from a data sending node to a data receiving node. In order to route data correctly via data links of a network and over nodes of the network connected by the data links routing strategies or so-called routing protocols representing routing strategies are employed. The most popular routing protocols are the Routing Information Protocol (RIP), the Enhanced Internet Gateway Routing Protocol (EIGRP), the Intermediate System-to-Intermediate System (IS-IS) and the Open Shortest Path First (OSPF) protocol. These protocols are used as so-called interior gateway protocols for routing of data in networks which are under a common network administration. Data networks (e.g. the INTERNET) do not have predefined data paths/connections between a sending node and a receiving node, in contrast to networks having fixed communication connections (e.g. telephone networks). Interior routing protocols are in general based on an approach wherein data communication from a sending node to a receiving node is not performed via predefined data links and nodes of the network. Instead, data or data packages are communicated from one node to another, wherein each routing decision which data link to the next node has to be chosen is “made up” by each node separately. Therefore, a node also referred to as router transmitting data to other nodes/routers does not “know” the complete data path or the data links forming the data path, respectively, for the communication of data from the sending node to the receiving node. Each node/router for itself make its own routing decision depending on its routing information to which next node/router the data or data packages thereof can be transmitted. As a consequence, the routing decision, i.e. the determination of the next node/router to which data is transmitted is made locally by the node/router communicating the respective data.
If the operation condition of each node/router within the network is known, it is possible to determine a data path and the data links forming the data path over which data or data packages thereof are communicated through the network. The operation condition of each node/router and, in particular, the routing decision of each node/router is determined via a cost function which determines the cost of the links. The cost function is protocol specific and can depend on the capacity of the links, the type and/or amount of data to be communicated, the utilization of data links to nodes to which data have to be transmitted, the (physical) delay and the data communication situation of the whole network. In practice the cost functions depend only on static and/or predefine variables like the capacity of the links and a delay value for the links which are once defined in the router database. Therefore if no errors in the network occur, the operating conditions of nodes/routers of a network do not vary during data communication, which makes it possible to determine the data path over which data will be communicated from the sending node to the receiving node.
A further fundamental principle of the interior routing protocols mentioned above is to always choose the shortest data path between a sending node and a receiving node. The routing protocols define a metric according to which the length of a data path is determined and information for the determination of the shortest data path are distributed over the network. For example, the Open Shortest Path First (OSPF) protocol commonly uses an additive metric based on time independent parameters such as the data communication capacity of data links (e.g. CISCO routers) or/and the delay for data communication over data links. In the OSPF-metric, the costs for each data link from a node/router to other nodes/routers connected thereto are inputted. Data communication parameters of a data link between a node/router to the next node/router can depend on the direction of data communication over the data link. Thus, the costs for data links may vary in relation to the data communication direction. The overall costs of a data path is obtained by a summation of all costs of the data links included by the data path.
The metric of the Enhanced Internet Gateway Routing Protocol (EIGRP) is more complicated than the metric of the OSPF-protocol but is mostly used in a form reduced to an additive metric.
The approach always to select the shortest data path implies a single-path routing, i.e. the routing between two nodes/routers is identical for all data flows. It is possible to define a multipath routing but for stability (e.g. loop protection) and protocol depended reasons (e.g. TCP performance degeneration in the case of reordered packets) it is rarely used. As a result of the fixed cost metric and the single path routing, congestions of data paths or single data links included of a data path may occur. This occurs for example if the amount of data is larger than the data communication capacity of single data links. Similar problems can occur if the data communication capacity of a node/router is not sufficient to communicate the desired amount of data, e.g. if the node/router is included by data paths of different sending nodes and/or different receiving nodes.
Furthermore, specific data paths and/or data links may be utilized very often, while other may be used only sometimes. This unequal distribution of data communication over the data links results in an unequal link utilization of the network data links. This unequal link utilization may also lead to congestions for different data links. Even in the case of high utilized links the network is not applicable for real time applications like IP telephony because of the nonlinear dependency between the load and the waiting time. Furthermore, such a routing of data in a network leads to an uneconomic operation of the network since data links, which are provided within the network requiring expensive hardware and software means, are not used.
The conventional approach to optimize routing of data in a network was to improve/enhance existing routing protocols or to develop new routing protocols. Since altered or new routing protocols must be established throughout the whole network, usually, altered or new hardware and software components are required. Therefore, this optimization is mainly limited due to organizational problems.